In the production of zeolites, particularly type 4A zeolite, the zeolite suspension resulting from known process steps is subjected to a treatment to separate solids from the washing and/or mother liquor in order to minimize costs, particularly energy costs, in the subsequent drying process.
In the process described in U.S. Pat. No. 4,041,135 and corresponding German Application No. 26 33 304, the zeolite suspension in the form of an aqueous mass is delivered through a pipe to a solids separation zone consisting of a circulating, porous belt. A controlled vacuum is applied at different points of the belt by means of a suitable vacuum source; the zeolite suspension being delivered onto the belt at a controlled speed by a distributor. The mother liquor and additionally supplied washing liquor are removed under suction from the zeolite suspension by means of suction boxes which are mounted to reciprocate below the porous filter belt in the direction of movement thereof, the arrangement being such that, in the event of a forward movement both of the filter belt and of the suction boxes, the suction boxes are connected to a vacuum source, whereas during the return movement of the suction boxes in the opposite direction to the filter belt, the suction boxes are ventilated. The removal under suction of the mother and washing liquors results in the formation on the filter belt of a partly dewatered filter cake which, at the ejection end of the filter belt, is removed therefrom and subsequently dried, preferably by spray drying. The dried product is in the form of a friable mass which can readily be reduced to a fine powder.
The filter cake obtained by means of the described vacuum belt filter contains approximately 50% of water with small amounts of mother or washing liquor. The drying of the filter cake leaving the vacuum belt filter with a liquid content of about 50% involves a high consumption of energy, for example, fuel gas in the case of spray drying.